This proposed research is concerned with an acoustical approach for estimating vocal-tract shapes. The main objective is to establish a recently developed method for estimating a human vocal tract shape (which is defined by a finite number of cross-sectional areas along the vocal tract from the glottis to the lips) from acoustic data. The method is a digital inverse filter based on the linear prediction of speech and requires only the speech sound itself as an input signal. Thus the potential hazard of x-rays is avoided and the cumbersome constraints imposed upon the subjects by other methods are eliminated. Seven specific problems (particularly, the most crucial problems of the energy losses within the vocal tract and of the excitation source characteristics) are to be studied to make the method truly applicable to various areas of speech research. These problems will be investigated by analysis and production models of the vocal tract together with some previously obtained x-ray data on vocal tract shapes. Potential applications of the research include detection of abnormalities and post-surgery speech rehabilitation for orofacial patients, and speech training aids for the deaf.